1. Field of the Invention
The present invention is directed to a ventilator of the type having a gas flow generator for generating a flow of gas at pre-adjustable pressure and/or flow rate, an inspiratory line with a proximal end connected to the gas flow generator and a distal end adapted for connection to a patient, an expiratory valve connected to the inspiratory line at a specific distance from the distal end of the inspiratory line to evacuate gas exhaled by the patient, a pressure gauge and/or a flow meter disposed to measure the pressure and/or flow rate of gas in the inspiratory line, and a control unit for controlling at least the maintenance of a positive end-expiratory pressure (PEEP).
2. Description of the Prior Art
A ventilator of the above type is described in PCT Application WO 94/06499. This known ventilator has an inspiratory line connected to a gas source at one end and to the patient at the other end. An expiratory valve is connected to the inspiratory line at a specific distance from the patient. In one embodiment, the expiratory valve is connected to a second gas source for the purpose of maintaining a pre-adjustable Positive End-Expiratory Pressure (PEEP). In another embodiment, the expiratory valve is instead connected to the gas source via a valve system in order to maintain PEEP. A pressure gauge and flow meter are arranged in the inspiratory line between the gas source and the expiratory valve. A control unit controls the entice ventilator. This known ventilator is primarily intended for use as a home care ventilator, i.e. a respirator a patient can use at home.
Another known ventilator is described in French Patent 2 724 322. This known ventilator has an inspiratory line connected to a gas source at one end and to the patient at the other end. An expiratory valve is connected to the inspiratory line at a specific distance from the patient. The expiratory valve can be regulated to maintain a pre-selected PEEP. A pressure gauge is arranged in the inspiratory line between the gas source and the expiratory valve. A volume meter can be arranged between the gas source and the expiratory valve, downstream of the expiratory valve or between the expiratory valve and the patient, for measuring inhaled and exhaled volumes, respectively. During expiration there is no flow from the gas source through the inspiratory line. This known ventilator also could be used as a home care ventilator.
Interest in home care ventilators is steadily increasing. This is because such a device is advantageous to the patient, who is able to be in her/his own home and can enjoy a greater degree of mobility. There are also public health benefits, since home care frees hospital resources by reducing in-patient treatment time, beds in intensive care being particularly costly. This type of ventilator can be battery-powered and is sometimes referred to as a `portable` ventilator. Despite this terminology, such a ventilator usually weighs quite a few kilograms and can only be carried around with some difficulty, even by healthy people.
A genuinely portable ventilator, i.e. a ventilator (weighing up to 1 kg, preferably less than 500 g) the patient is easily able to carry, with a capacity sufficient to provide respiratory assistance for several hours, would be even more desirable for patients. Miniaturizing a ventilator to this extent, employing modern turbine, battery and microprocessor technology etc., is thoroughly feasible. One important factor in this process would be to retain every essential function available in a conventional ventilator, such as the ability to maintain a PEEP, to as large an extent as possible. Such a fully portable ventilator would be suitable for virtually every kind of patient. It even could be used as an emergency ventilator for a number of applications and could be included in the basic equipment of e.g. aircraft, buses, boats, ambulances, fire engines, etc.
The relative complexity of the way in which PEEP is maintained is a shortcoming of the first described known ventilator described above, since it utilizes a second source of gas or a valve system formed by a number of valves.